Hitler’s generals and admirals could not get him the transport or protect them to cross the channel. Would have taken more than the Normandy invasion. Even Hitler had enough sense not to overrule his generals and to attempt it.
When you put it in that perspective, it becomes obvious. The British land forces would have been much weaker than the Werhmacht, since they left their equipment at Dunkirk. OTOH the RAF was a lot stronger in 1940 than the Luftwaffe was in 1944, and in 1940 the Royal Navy was also more powerful than the 1944 Kriegsmarine (tho the issue would have been decided primarily by the contest between the Luftwaffe and the RAF). It was far too close to being a fair fight to have been an attractive option for the German military.